Extracted, cooled, compressed/intercooled, cooling/combustion air for a gas turbine engine

ABSTRACT

A system for cooling hot section components of a gas turbine engine. The cooling system includes a plurality of compressors, or compression train, and an intercooler disposed between each adjacent pair of compressors so as to achieve the desired pressure and temperature of the cooling air at reduced shaft power requirements. The first stage of compression may be provided by the booster, or low pressure compressor, of the engine, with the first intercooler receiving all of the air discharging from the booster. After exiting the first intercooler, a first portion of the booster discharge air is routed to the engine high pressure compressor and a second portion is routed to an inlet of the second compressor of the cooling air compression train. The compressed, cooled air exiting the last, downstream one of the compressors is used for cooling at least a first hot section component of the engine.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to gas turbine engines, and moreparticularly, to a system for supplying extracted, cooled,compressed/intercooled, cooling and combustion air for gas turbineengines.

2. Related Art

The highest temperatures in gas turbine engines are typically found inthe combustor and the turbines. The continuing demand for larger andmore efficient gas turbine engines creates a requirement for increasedturbine operating temperatures. However, as the combustor and turbinehot gas temperatures have been increased to achieve increased output andthermal efficiencies, the challenge to maintain component lives, due tothe metallurgical limitations of critical hot components such as theturbine rotor blades and disks, as well as the challenge to control NOxemission levels has also increased.

Conventional air-cooled gas turbine engines typically extract coolingair from one or more stages of the high pressure compressor to providecooling for elements of the combustor and high pressure turbine. Amongthe more recent of the known systems for providing cooling air tocritical hot section components are those shown in U.S. Pat. Nos.5,305,616 and 5,392,614, each issued to Coffinberry and assigned to theassignee of the present invention, each of which is expresslyincorporated by reference herein in its entirety. Each of the variousembodiments disclosed in the Coffinberry patents utilizes a first streamof cooling air extracted from the discharge of the high pressurecompressor which is further compressed using a turbocompressor andcooled in a heat exchanger prior to cooling elements of the highpressure turbine and combustor. The turbine section of theturbocompressor is driven by air extracted from a mid-stage of the highpressure compressor. Other known systems utilizing a turbocompressor tofurther compress and cool extracted air from a high pressure compressorof a gas turbine engine have included a heat exchanger disposed betweenthe compressor and turbine sections of the turbocompressor such that theinlet to the heat exchanger is in fluid flow communication with theoutlet of the compressor section and the outlet of the heat exchanger isin fluid flow communication with the inlet of the turbine section. Whilesuch systems advantageously provide cooling air having a higher pressureand cooler temperature then would otherwise be available to hot sectioncomponents, such systems are subject to the following disadvantages.Compressor discharge air is relatively expensive air, in terms of engineperformance, and additionally is relatively difficult to furthercompress as compared to a lower pressure source of cooling air.Accordingly, gas turbine engine designers continue to search for new andimproved cooling air systems, with issues including system pressuredrop, compression power requirements, heat exchanger costs andreliability, and equipment size and weight, etc.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a system for coolingat least a first portion of a gas turbine engine having a compressor anda core gas stream. According to a preferred embodiment, the coolingsystem comprises a plurality of compressors disposed in serial flowrelationship with one another and effective for compressing air. Each ofthe compressors has an inlet and an outlet, with an inlet of a first,upstream one of the compressors receiving air having a pressure which isless than or equal to a pressure of the core gas stream of the engine atan entrance to the high pressure compressor of the engine. The upstreamcompressor produces a first compressed airflow. The cooling systemfurther comprises a first intercooler effective for reducing atemperature of the first compressed air flow. The first intercoolerincludes a first inlet and a first outlet for the first compressedairflow which receives cooling from the first intercooler. The firstinlet is in fluid flow communication with the outlet of the upstreamcompressor and the first outlet of the first intercooler is in fluidflow communication with the inlet of a second one of the compressors.The first intercooler further includes a second inlet and a secondoutlet for a first coolant fluid providing cooling to the firstintercooler. The airflow discharging from a last, downstream one of thecompressors is used for cooling at least a first portion of the engine.

BRIEF DESCRIPTION OF THE DRAWINGS

The structural features and functions of the present invention willbecome more apparent from the following detailed description of thepreferred embodiments when taken in conjunction with the accompanyingdrawings in which:

FIG. 1 is a block diagram of a gas turbine engine incorporating acooling system according to the present invention;

FIG. 2 is a block diagram of the gas turbine engine shown in FIG. 1 andthe cooling system of the present invention according to an alternativeembodiment;

FIG. 3 is a block diagram of the gas turbine engine shown in FIG. 1 andthe cooling system of the present invention according to anotheralternative embodiment;

FIG. 4 is a block diagram of the gas turbine engine shown in FIG. 1 andthe cooling system of the present invention according to anotheralternative embodiment.

DETAILED DESCRIPTION

Referring now to the drawings, FIG. 1 is a block diagram of a gasturbine engine 10 incorporating an engine cooling system indicatedgenerally at 12, according to the present invention. The exemplary gasturbine 10 illustrated in FIG. 1 is derived from a turbofan engine ofthe type used to propel aircraft, and may be used in either marine orindustrial applications. Engine 10 includes, in serial flowrelationship, a booster or low pressure compressor 14, a high pressurecompressor 16, a combustor 18, a high pressure turbine 20 and a lowpressure turbine 22. The high pressure turbine 20 is drivingly connectedto the high pressure compressor 16 with a first rotor shaft 24 and thelow pressure turbine 22 is drivingly connected to the low pressurecompressor 14 with a second rotor shaft 26 coaxially disposed withinshaft 24 about a longitudinal centerline axis of engine 10. Engine 10may be used to drive a load 28, which may comprise a marine propeller oran industrial gas generator for instance. Load 28 may be disposedafterward of engine 10 as shown in solid in FIG. 1, with load 28drivingly coupled to an aft extension 30 of the rotor shaft 26, oralternatively, load 28 may be disposed forward of engine 10 as shown inphantom in FIG. 1 with load 28 coupled to a forward extension 32 ofshaft 26. Engine 10 may be alternatively configured to include anintermediate turbine (not shown) disposed longitudinally or axiallybetween high pressure turbine 20 and low pressure turbine 22. With thisconfiguration, the intermediate turbine is drivingly connected to thelow pressure compressor 14 via shaft 26 and low pressure turbine 22comprises a power turbine which is disconnected from shaft 26, whereinthe aft extension 30 of shaft 26 is replaced by a separate shaftconnecting turbine 22 and load 28. It is noted that, unlike a turbofanengine, engine 10 does not include a fan disposed upstream of lowpressure compressor or booster 14.

The low pressure compressor 14 includes an inlet 34 which receivesambient air 36 which is compressed by compressor 14, so as to increasethe pressure and temperature of the ambient air. An outlet 38 ofcompressor 14 is in fluid flow communication with a first inlet 40 of anintercooler, or heat exchanger 42, with an entire portion of thecompressed airflow discharging through outlet 38 of compressor 14passing through a duct 44 to the first inlet 40 of intercooler 42. It isnoted that although the term "intercooler" may be used in the art todenote a heat exchanger positioned flow-wise between two compressors, inthe present context the term intercooler refers to a heat exchangerwhich is positioned between two components which may comprise twoflow-wise adjacent compressors, or alternatively which may comprise alast, downstream compressor of one of the illustrated cooling systems ofthe present invention and a component of engine 10 such as high pressureturbine 20. Duct 40 may be relatively large in size so as to accommodateall of the compressed airflow discharging from compressor 14 and may beconfigured to comprise a scroll duct so as to accommodate thepositioning of intercooler 42 mounted off of engine 10. Intercooler 42is effective for reducing a temperature of the compressed airflow fromduct 44 which flows through intercooler 42 along a flowpath 46 betweeninlet 40 and a first outlet 48 of intercooler 42. Intercooler 42 maycomprise a conventional counterflow heat exchanger and includes a secondinlet 50 and a second outlet 52 for a coolant fluid providing cooling tointercooler 42 so as to reduce the temperature of the compressed airflowfrom duct 44. In the embodiment illustrated in FIG. 1, the coolant fluidas illustrated as comprising ambient air which may be forced by aconventional blower 54 through a duct 56 to the second inlet 50 ofintercooler 49. The ambient air then flows through intercooler 42 alongpath 58 discharging through outlet 52 to ambient via a duct 60. Thetemperature of the ambient air is less than a temperature of thecompressed airflow entering intercooler 42 from duct 44 and thereforeresults in a reduction of the temperature of the compressed airflow fromthe low pressure compressor 14. Alternatively, the coolant fluidprovided to intercooler 42 may comprise water or fuel, with conventionalmeans such as pumps used to provide the fluid to the second inlet 50 ofintercooler 42. If fuel is used, the fuel discharging through the secondoutlet 52 may be routed to combustor 18, with the heat added to the fuelas it passes through intercooler 42 being added to engine 10. As afurther alternative, a fuel/water heat exchanger (not shown) may be usedin conjunction with intercooler 42. In this instance, water is providedto the second inlet 50 of intercooler 42 and flows through intercooler42 providing cooling to the compressed airflow from duct 44. Afterdischarging from the second outlet 52 of intercooler 42 the water isducted to the fuel/water heat exchanger where it receives cooling. Thewater is then returned to the second inlet 50 of intercooler 42,providing a closed loop system. Cooling is provided to the fuel/waterheat exchanger by the fuel, which may be routed to combustor 18 afterexiting the fuel/water heat exchanger. By providing such an arrangement,the cooling capacity of available fuel may be utilized while avoidingany risk of hot air contacting fuel within intercooler 42.

The cooling system 12 further includes second and third compressorscomprising, respectively, a first auxiliary compressor 62 and a secondauxiliary compressor 64. Each of the auxiliary compressors 62 and 64 isdriven by a power source 66. In the illustrative embodiment shown inFIG. 1, power source 66 comprises an auxiliary turbine which is coupledto each of the auxiliary compressors 62 and 64 via a shaft 68. Turbine66 includes an inlet 70 which is in fluid flow communication with highpressure compressor 16, preferably a mid-stage of compressor 16, via aduct 72. The air from high pressure compressor 16 is used to driveturbine 66 and in the process is cooled as it expands through turbine 66in a conventional manner. This air then discharges turbine 66 through anoutlet 74 and may be routed to the low pressure turbine 22 through aduct 76 for purposes of cooling turbine 22. Alternatively, power source66 may comprise an electric motor or other conventional means ofproviding motive power to auxiliary compressors 62 and 64. Afterdischarging from the first outlet 48 of intercooler 42, the compressedairflow produced by low pressure compressor 14 is split into a firstportion which is in fluid flow communication with an inlet 79 of thehigh pressure compressor 16 via duct 78 and a second portion which is influid flow communication with an inlet 80 of the first auxiliarycompressor 62 via a duct 82. It should be understood that the massflowrate of the second portion of air passing through the duct 82 issignificantly less than the mass flowrate of air passing through duct 78and entering inlet 79 of high pressure compressor 16. The air enteringhigh pressure compressor 16 comprises the primary or core gas stream ofengine 10 and is further compressed by compressor 16. The core gasstream of engine 10 then enters combustor 18 where the pressurized airis mixed with fuel, provided to combustor 18 via duct 19, and burned toprovide a high energy gas stream, in a conventional manner. This highenergy gas stream then enters, in succession, the high pressure turbine20 and the low pressure turbine 22 where the gas stream is expanded andenergy is extracted to operate the high pressure compressor 16 and thelow pressure compressor 14, as well as to drive load 28.

The air entering auxiliary compressor 62 through inlet 80 is furthercompressed and discharges compressor 62 through an outlet 84 with ahigher pressure and temperature than the compressed air streamdischarging intercooler 42. Outlet 84 of compressor 62 is in fluid flowcommunication with a first inlet 86 of a second intercooler, or heatexchanger 88 via a duct 85. The compressed airflow entering inlet 86flows through intercooler 88, so as to receive cooling from intercooler88, along a flow path 90 and discharges intercooler 88 through a firstoutlet 92. Intercooler 88 further includes a second inlet 94 and asecond outlet 96 for a coolant fluid providing cooling to intercooler88. The coolant fluid may alternatively comprise air, water or fuel andis supplied to the second inlet 94 of intercooler 88 via duct 98 andthen flows through intercooler 88 along flowpath 100 and dischargesthrough the second outlet 96 of intercooler 88 into duct 102. If thecoolant fluid comprises fuel, duct 102 may be routed to combustor 18 soas to utilize the heat added to the fuel as it passes throughintercooler 88. As with intercooler 42, intercooler 88 may comprise aconventional counterflow heat exchanger. The first outlet 92 ofintercooler 88 is in fluid flow communication with an inlet 104 of thesecond auxiliary compressor 64, via duct 106. The air enteringcompressor 64 through inlet 104 is further compressed and dischargescompressor 64 through an outlet 108. The outlet 108 of auxiliarycompressor 64 is in fluid flow communication with the high pressureturbine 20 via duct 109. The compressed air passing through duct 109 tohigh pressure turbine 20 may be used for cooling various components ofthe high pressure turbine 20 such as the stage 1 nozzles (not shown). Aportion of the air discharging compressor 64 may optionally be directedto combustor 18 through duct 110, for purposes of cooling elements ofcombustor 18 such as a liner (not shown) of combustor 18. Any air usedto cool the liner of combustor 18 may then be injected at a premixer(not shown) of combustor 18 to lean a combustor dome (not shown)fuel/air mixture. A though the cooled, compressed air discharging fromcompressor 64 may be provided to the high pressure turbine 20 andcombustor 18 via separate ducts in a parallel flow configuration, asshown in FIG. 1, the cooled, compressed air may be provided to highpressure turbine 20 and combustor 18 in a series flow configuration (notshown). In such a configuration, the compressed air may be routed tohigh pressure turbine 20 via a duct such as duct 109 and may then berouted to elements of combustor 18, such as the liner of combustor 18,after flowing through elements of turbine 20, such as the stage 1nozzles of turbine 20. For a more detailed discussion of the manner inwhich cooling air may flow first through the stage 1 high pressureturbine nozzles and then through the combustor liner, the reader mayrefer to copending and commonly assigned U.S. Patent Applicationentitled "Regenerative Combustor Cooling In a Gas Turbine Engine"(Attorney Docket No. 13DV-11660).

In operation, ambient air is received and compressed by the low pressurecompressor 14, which comprises an upstream compressor of cooling system12, and the compressed airflow is then routed through intercooler 42where the temperature of the compressed air is reduced. A first, largerportion of the air discharging through the outlet 48 of intercooler 42is routed to the inlet 79 of the high pressure compressor 16 throughduct 78, so as to provide the core gas stream of engine 10. A second,smaller portion of the air discharging intercooler 42 is compressed insuccession by auxiliary compressors 62 and 64 and further cooled byintercooler 88 after discharging from compressor 62 and prior toentering compressor 64. Compressor 64 comprises a last, or downstreamcompressor of cooling system 12. The air discharging auxiliarycompressor 64 is then routed to the high pressure turbine 20, via duct109, where it is used for cooling components of the high pressureturbine 20 such as the stage 1 nozzles. A portion of the air dischargingauxiliary compressor 64 may also be routed to combustor 18, via duct110, where it may be used for cooling elements of the combustor 18 suchas the combustor liner. Alternatively, the cooling air may flow firstthrough the stage 1 nozzles of high pressure turbine 20 and then throughthe liner of combustor 18, in a series flow arrangement, as discussedpreviously. The use of the three stages of compression provided by lowpressure compressor 14, and auxiliary compressors 62 and 64, as well asthe cooling provided by intercoolers 42 and 88 provides cooling air foruse to the high pressure turbine 20 of engine 10 which is of a higherpressure and lower temperature then would otherwise be available. Thespecific magnitude of the pressure and temperature of the cooling airprovided to the high pressure turbine is dependent upon the particularapplication and the sizing of each compressor and intercooler. However,the magnitude of the incremental pressure and temperature, relative tothat of conventional cooling, may be similar to that stated in theillustrative examples provided in U.S. Pat. Nos. 5,392,614 and5,305,616. The use of cooling system 12 is particularly advantageouswhen applied to an engine incorporating series flow of cooling airthrough the high pressure turbine stage 1 nozzles and combustor liner,as discussed in detail in the copending and commonly assigned U.S.Patent Application having Attorney Docket 13DV-11660. This is the casesince the increased pressure of the cooling air of system 12, relativeto that of prior conventional cooling systems, permits such a seriesflow arrangement while maintaining sufficient cooling air pressure sothat the cooling air may then be injected at the premixer of combustor18 so as to lean the combustor dome fuel/air mixture which results in areduction of the adiabatic flame temperature and attendant Zeldovich NOxemissions.

Referring now to FIG. 2, an alternative cooling system 112 according tothe present invention is illustrated. Cooling system 112 is identical tocooling system 12 with the following exceptions. The second auxiliarycompressor 64 shown in the embodiment of cooling system 12 is notutilized in cooling system 112, with only two stages of compressionprovided by the low pressure compressor 14 and the first auxiliarycompressor 62, which comprises the last, downstream compressor ofcooling system 112, for the air which is routed to high pressure turbine20 and combustor 18 for cooling. In the present context a "stage ofcompression" is intended to refer to the compression provided by any ofthe various compressors included in the disclosed cooling systems, suchas low pressure compressor 14 and auxiliary compressors 62 and 64.However, it should be understood that at least low pressure compressor14 may comprise a "multi-stage", axial flow compressor as is typicallyused in engine 10, with "multi-stage" referring to a plurality ofalternating rows of stationary vanes and rotating blades mounted ondisks. Additionally, while low pressure compressor 14 and auxiliarycompressors 62 and 64 may comprise axial flow compressors, each of thecompressors 14, 62 and 64 may comprise a radial flow compressor. Anotherdifference between cooling systems 12 and 112 is that the secondintercooler 88 may be deleted in cooling system 112, with the outlet 84of the first auxiliary compressor 62 being in direct fluid flowcommunication with at least the high pressure turbine 20 via a duct (notshown). Alternatively, intercooler 88 may be disposed between auxiliarycompressor 62 and high pressure turbine 20, with the outlet 84 ofcompressor 62 in fluid flow communication with the first inlet 86 ofintercooler 88 via duct 85, in the same manner as shown in FIG. 1 forcooling system 12. The only difference with respect to intercooler 88 incooling system 112 is that the first outlet 92 of intercooler 88, whichis used to discharge the compressed airflow from auxiliary compressor62, is direct fluid flow communication with the high pressure turbine20, via a duct 114 as shown in FIG. 2, rather than with the secondauxiliary compressor 64 which is not used. A portion of the airdischarging intercooler 88 may optionally be supplied to combustor 18via duct 115. Although the coolant fluid provided to the second inlet 94of intercooler 88 may alternatively comprise air, water or fuel, fuel isthe preferable source of coolant fluid with the fuel discharging fromthe second outlet 96 of intercooler 88 in fluid flow communication withcombustor 18 via a duct 116 as shown in FIG. 2. The operation of coolingsystem 112 is the same as that described previously with respect tocooling system 12 with the exception that fewer stages of compression,and possibly fewer stages of intercooling, are provided for thecompressed airflow ultimately routed to the high pressure turbine 20 andoptionally to combustor 18 for purposes of cooling. Consequently, theair provided to the high pressure turbine 20 and combustor 18 may be ofa lower temperature than that provided previously with respect tocooling system 12. Although three stages of compression have beenillustrated with respect to cooling system 12 and two stages ofcompression has been illustrated with respect to cooling system 112,regarding the compressed airflow provided for cooling to high pressureturbine 20 and combustor 18, it should be understood that additionalstages of compression and intercooling may be used for the coolingairflow provided to engine 10. The particular compression trainconfiguration is selected, based upon tradeoff studies, which providesthe highest compression efficiency with the least equipment and theassociated costs, consistent with the cooling air requirements for theparticular application of engine 10. In some instances compressionefficiency may not be maximized so as to maintain equipment costs withindesirable limits. Although additional stages of compression may beutilized, the additional gain in compression efficiency may be marginalas explained in U.S. Pat. No. 4,751,814 to Farrell, which is assigned tothe assignee of the present invention and is incorporated by referenceherein in its entirety.

Referring now to FIG. 3, a cooling system 212 is illustrated accordingto an alternative embodiment of the present invention. Cooling system212 is the same as cooling system 12, with the following exceptions.Heat exchanger 42 of system 12 is omitted from cooling system 212 andaccordingly, all of the air discharging from the low pressure compressor14 is routed directly to the high pressure compressor 16, in aconventional manner. The auxiliary compressors 62 and 64 and intercooler88 are configured, and function as described previously with respect tocooling system 12 except that auxiliary compressor 62 now comprises thefirst, or upstream compressor in the compression train, or series ofcompressors of cooling system 212, and ambient air 36 is received by theinlet 80 of auxiliary compressor 62. Ambient air 36 also enters theinlet 34 of the low pressure compressor 14 of engine 10. Anotherdifference between cooling systems 212 and 12, is that in cooling system212 the outlet 108 of auxiliary compressor 64 is in fluid flowcommunication with an inlet 214 of a second intercooler 216, with thecompressed airflow discharging from the second auxiliary compressor 64flowing to intercooler 216 via a duct 218. The compressed airflowentering intercooler 216 travels along a path 220, thereby receivingcooling from intercooler 216, and discharges through a first outlet 222of intercooler 216. Intercooler 216 further includes a second inlet 224and a second outlet 226 for a coolant fluid flowing through intercooler216 along path 228 so as to provide cooling to intercooler 216. Thecoolant fluid is supplied to inlet 224 via duct 230, and may compriseair, water or fuel. The coolant fluid discharges intercooler 216 throughduct 232, which is in fluid flow communication with combustor 18 if thecoolant fluid used is fuel. The first outlet 222 of intercooler 216 isin fluid flow communication with an inlet 234 of a third auxiliarycompressor 236, which comprises a last, downstream compressor of coolingsystem 212. As with auxiliary compressors 62 and 64, auxiliarycompressor 236 may comprise either an axial flow or a radial flowcompressor. The compressed, cooled airflow discharging from intercooler216 flows to inlet 234 of compressor 236 via a duct 238. The compressed,cooled air entering compressor 236 is then further compressed and thendischarges compressor 236 through an outlet 240. Outlet 240 ofcompressor 236 is in fluid flow communication with at least the highpressure turbine 20, with the compressed airflow ducted to turbine 20via a duct 242. The outlet 240 of compressor 236 may further be in fluidflow communication with the combustor 18 of engine 10, with a portion ofthe compressed airflow discharging from compressor 236 ducted tocombustor 18 via a duct 244. Any cooling air ducted to combustor 18 maybe utilized as described previously with respect to system 12. Each ofthe auxiliary compressors 62, 64 and 236 are driven by the power source66, which may comprise an auxiliary turbine configured as shown in FIG.3, or alternatively may comprise an electric motor or other conventionalmeans of supplying motive power to the compressors 62, 64 and 236 via atleast one shaft 68.

In operation, ambient air 36 is compressed, in succession, by auxiliarycompressors 62, 64 and 236, with the compressed airflow being cooled byintercoolers 88 and 216 between adjacent stages of compression, so as toprovide the desired pressure and temperature of the compressed coolingairflow provided to elements of high pressure turbine 20 and optionallyto elements of combustor 18. As with cooling system 12, the compressedcooling airflow of cooling system 212 may be provided to elements ofhigh pressure turbine 20 and combustor 18 in either a parallel flow orseries flow configuration. Ambient air 36 also enters the inlet 34 oflow pressure compressor 14 and is compressed in succession bycompressors 14 and 16, and mixed with fuel and burned in combustor 18 soas to create a high energy gas stream which is then expanded throughturbines 20 and 22.

Referring now to FIG. 4, a cooling system 312 according to analternative embodiment of the present invention is illustrated. Coolingsystem 312 is the same as cooling system 212 with the followingexceptions. Cooling system 312 does not include the third auxiliarycompressor 236, but instead includes only upstream auxiliary compressor62 and downstream auxiliary compressor 64, with ambient air 36 enteringthe inlet 80 of auxiliary compressor 62. Ambient air 36 also enters theinlet 34 of the low pressure compressor 14 of engine 10 and flowsthrough engine 10 as discussed previously with respect to cooling system212. Another difference between systems 312 and 912 is that in system312 intercooler 916 is positioned flow-wise between the second, and lastauxiliary compressor 64 and at least the high pressure turbine 20 ofengine 10. The compressed airflow discharging compressor 64 throughoutlet 108 and duct 218 is provided to the first inlet 214 ofintercooler 216, as with cooling system 212. Additionally, the coolantfluid is provided to the second inlet 224, as discussed previously withrespect to cooling system 212. However, the first outlet 222 ofintercooler 216 is now in direct fluid flow communication with at leastthe high pressure turbine 20, rather than being in fluid flowcommunication with the inlet 234 of the third auxiliary compressor 236which is not used in cooling system 312. Outlet 222 of intercooler 216may optionally also be in fluid flow communication with combustor 18. Atleast a portion of the compressed airflow discharging intercooler 216through the first outlet 222 is ducted to the high pressure turbine 20via a duct 314 and a second, optional portion may be ducted to thecombustor 18 via duct 316. It is further noted that the use ofintercooler 216 in cooling system 312 is optional, with the use ofintercooler 216 dependent upon the particular application of coolingsystem 312. In certain applications, the outlet 108 of the secondauxiliary compressor 64 may be in direct fluid flow communication withat least the high pressure turbine 20 and optionally, combustor 18. Withthe exception of the deletion of the third auxiliary compressor 236 andthe optional use of intercooler 216, the operation of cooling system 312is otherwise the same as that discussed previously with respect tocooling system 212.

In operation, any of the cooling systems of the present invention may beused to provide high pressure, cooled cooling air to a first portion ofengine 10, such as the high pressure turbine 20, and additionally to asecond portion of engine 10, such as combustor 18, so as to achieveincreased cooling of elements of turbine 20 and combustor 18.Additionally, the various embodiments of the present invention may beused to provide cooling air at a pressure significantly higher thanotherwise available thereby permitting a series flow of the cooling airthrough elements of turbine 20 and combustor 18. The increased coolingof elements of turbine 20 and combustor 18 may be accomplished whileminimizing injection of cooling air ahead of the inlet of the rotor (notshown) of high pressure turbine 20 by injecting at least a portion ofthe cooling air at the premixer of combustor 18. This feature raises theinlet temperature of the rotor of high pressure turbine 20 at which drylow NOx emissions requirements can be achieved since the dome fuel/airmixture is reduced, thereby reducing the adiabatic flame temperature andattendant Zeldovich NOx emissions. The arrangement of the compressorsand intercoolers of the various embodiments of the present inventionreduces the shaft horsepower necessary to accomplish the overallcompression of the cooling air to a given level above the discharge ofthe high pressure compressor 16, and provides cooling air at atemperature significantly lower than otherwise available with thecooling air of conventional systems utilizing simple extraction pointsin compressor 16 to provide cooling air. Additionally, if coolingsystems 12 or 112 are utilized a further advantage is realized since thefirst level of compression is accomplished by the highly efficient lowpressure compressor 14 of engine 10, thereby reducing the additionalequipment required to further compress the cooling air. A furtherreduction in equipment may be realized when either of cooling systems 12or 112 of the present invention is applied to an engine having anintercooled compressor cycle configuration such as engine 10 in FIGS. 1and 2. In these instances the first stage of intercooling of systems 12and 112 is also existing in the overall cycle arrangement of engine 10and is provided by an intercooler such as intercooler 42.

While the foregoing description has set forth the preferred embodimentsof the invention in particular detail, it must be understood thatnumerous modifications, substitutions and changes can be undertakenwithout departing from the true spirit and scope of the presentinvention as defined by the ensuing claims. For instance, although thecooling system of the present invention has been illustrated in variousembodiments in conjunction with a gas turbine engine comprising aderivative of a turbofan engine, the cooling system of the presentinvention may further be used with a turbofan engine, or with anindustrial gas turbine engine which is not derived from a turbofanengine and may therefore be made of a heavier construction than thatnormally associated with turbofan engines. Additionally, although thecooling air produced by the cooling system of the present invention hasbeen illustrated for use with the high pressure turbine and combustor,it may further be utilized with other hot section components such as thelow pressure turbine, an intermediate turbine or a power turbine, orwith internal or external clearance control systems. The invention istherefore not limited to specific preferred embodiments as described,but is only limited as defined by the following claims.

What is claimed is:
 1. A system for cooling at least a first portion ofa gas turbine engine having a high pressure compressor and a core gasstream, said cooling system comprising:a plurality of compressorsdisposed in serial flow relationship with one another and effective forcompressing air, each of said compressors having an inlet and an outlet,wherein said inlet of a first, upstream one of said compressors receivesair having a pressure which is less than or equal to a pressure of thecore gas stream at an entrance to the high pressure compressor of theengine, said upstream compressor producing a first compressed airflow,said upstream compressor comprising a low pressure compressor of theengine, and a second compressor comprising a first auxiliary compressorproducing a second compressed airflow; a first intercooler effective forreducing a temperature of said first compressed airflow, said firstintercooler having a first inlet and a first outlet for said firstcompressed airflow receiving cooling from said first intercooler, saidfirst inlet in fluid flow communication with said outlet of saidupstream compressor and said first outlet in fluid flow communicationwith said inlet of said second compressor, said first intercoolerfurther including a second inlet and a second outlet for a first coolantfluid providing cooling to said first intercooler, said first compressedairflow received by said first inlet of said first intercoolercomprising an entire portion of the airflow discharging through saidoutlet of said low pressure compressor of the engine, said firstcompressed airflow discharging from said first outlet of said firstintercooler split into a first portion in fluid flow communication withthe high pressure compressor of the engine and a second portion in fluidflow communication with said inlet of said first auxiliary compressor;wherein an airflow discharging from a last, downstream one of saidcompressors is used for cooling said at least a first portion of theengine.
 2. The cooling system as recited in claim 1, wherein:said last,downstream compressor comprises a second auxiliary compressor; saidcooling system further includes a second intercooler having a firstinlet and a first outlet for said second compressed airflow receivingcooling from said second intercooler, said first inlet of said secondintercooler in fluid flow communication with said outlet of said firstauxiliary compressor, said first outlet of said second intercooler influid flow communication with said inlet of said second auxiliarycompressor; said second intercooler further includes a second inlet anda second outlet for a second coolant fluid providing cooling to saidsecond intercooler; said outlet of said second auxiliary compressor isin fluid flow communication with said at least a first portion of theengine.
 3. The cooling system as recited in claim 1, wherein: said firstauxiliary compressor is said last, downstream compressor.
 4. The coolingsystem as recited in claim 3, further comprising:a second intercoolerhaving a first inlet and a first outlet for said second compressedairflow receiving cooling from said second intercooler, said first inletof said second intercooler in fluid flow communication with said outletof said first auxiliary compressor, said first outlet of said secondintercooler in fluid flow communication with said at least a firstportion of the engine; wherein said second intercooler further includesa second inlet and a second outlet for a second coolant fluid providingcooling to said second intercooler.
 5. The cooling system as recited inclaim 4, wherein:said second coolant fluid comprises fuel; said secondinlet of said second intercooler is in fluid flow communication with asource of said fuel; said second outlet of said second intercooler is influid flow communication with a combustor of the engine.
 6. The coolingsystem as recited in claim 1, further comprising:an auxiliary powersource; wherein said low pressure compressor is driven by a turbine ofthe engine and remaining ones of said plurality of compressors aredriven by said auxiliary power source.
 7. The cooling system as recitedin claim 6, wherein:said at least a first portion of the enginecomprises a high pressure turbine of the engine; said auxiliary powersource comprises an auxiliary turbine, said auxiliary turbine having aninlet in fluid flow communication with the high pressure compressor ofthe engine and an outlet in fluid flow communication with a low pressureturbine of the engine for cooling the low pressure turbine; saidauxiliary turbine is coupled to said remaining ones of said plurality ofcompressors via at least one shaft.
 8. The cooling system as recited inclaim 6, wherein said auxiliary power source comprises an electric motorcoupled to said remaining ones of said plurality of compressors via atleast one shaft.
 9. The cooling system as recited in claim 2,wherein:said second coolant fluid is selected from the group consistingof air, water and fuel.